1 Ganglia-groups of neuron cell bodies that lie peripheral to the central nervous system in vertebrates. 2  Bipolar neurons-cell body located near the middle of the axon; characteristic of retinal neurons. 3  Unipolar neurons-cell body lies off to one side of axon; characteristic of sensory neurons.
The principal host for diamonds are rocks formed in the earth's mantle that are known as eclogite and peridotite that are carried to the earth's surface in magmas known as kimberlit e and lamproite.
How Gemstones are Formed. Minerals form under various conditions in the earth. Most gemstones form in the Earth's crust; the top layer of the Earth, with a depth of 3 to 25 miles. Only two gemstone varieties-diamond and peridot-form in the Earth's mantle, which represents 80% of the Earth's volume.ow Gemstones are Formed. Minerals form under various conditions in the earth. Most gemstones form in the Earth's crust; the top layer of the Earth, with a depth of 3 to 25 miles. Only two gemstone varieties-diamond and peridot-form in the Earth's mantle, which represents 80% of the Earth's volume.